1. Field of the Invention
The present invention relates to a motorcycle provided with a valve-operating mechanism for actuating a valve which opens and closes a combustion chamber of an internal combustion engine, particularly to a motorcycle whose valve-operating mechanism includes biasing means for biasing the valve toward a valve closing direction and drive means for driving the valve toward a valve opening direction against the biasing means.
2. Description of the Related Art
In order to correspond to high-speed rotation of the internal combustion engine mounted on the motorcycle, several new technologies are known as follows.
One is a multi-valve structure in which the number of valves per cylinder, that is, the numbers of inlet valves and exhaust valves are increased. Other one is a gas spring type valve-operating mechanism in which compressible gas such as compressed air is used instead of a coil spring as means for biasing the valve toward the valve closing direction (for example, see Japanese Patent Laid-Open Publication No. 8-144772).
The gas spring type valve-operating mechanism has a better capability of following valve opening and closing timing than that of a coil spring type valve-operating mechanism. Additionally, in the gas spring type valve-operating mechanism, generation of machine noise at a high-speed rotation can be suppressed.
In the gas spring type valve-operating mechanism, the need for always filling a gas spring chamber with the compressed gas arises in order to maintain a predetermined compression repulsive force generated by the compressed gas. Therefore, the gas spring type valve-operating mechanism disclosed in Japanese Patent Laid-Open Publication No. 8-144772 includes a compressed-gas container (compressed-air container) or a gas compressor driven by a cam shaft.
In the case where the gas spring type valve-operating mechanism includes the compressed-gas container, the need for providing a drive means does not arise unlike the case where the gas spring type valve-operating mechanism includes the gas compressor. Therefore, the machine noise caused by the drive means is not generated. Additionally, the gas spring type valve-operating mechanism including the compressed-gas container has an advantage from the viewpoint of cost. However, the need for increasing a volume of the compressed-gas container arises when the predetermined compression repulsive force generated by the compressed gas is maintained for a long time.
The motorcycle has a larger exposed portion than an automobile, and the motorcycle has a less storage space for various components and accessories. Therefore, in the case the compressed-gas container having a large capacity is mounted on the motorcycle, not only it is necessary to maintain strength for withstanding a compressed gas pressure, but also it is necessary to make consideration of a contact with an object outside the body, which results in a problem in that the structure becomes complicated to increase production cost while a weight of the compressed-gas container is increased.